feat(solutions): add acronyms/cs/function

challenges/acronyms/solutions/cs/function/README.md

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+# acronyms/cs/function
+
+Created by [@Divlo](https://github.com/Divlo) on 5 September 2021.

challenges/acronyms/solutions/cs/function/Solution.cs

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+using System;
+
+namespace Solution
+{
+    class Program
+    {
+        static void Main()
+        {
+            string line = Console.ReadLine();
+            string[] words = line.Replace("\"", "").Split(' ');
+            string result = "";
+            foreach (string word in words)
+            {
+                result += word[0].ToString().ToUpper();
+            }
+            Console.WriteLine(result);
+        }
+    }
+}